1. Field of the Invention
The present invention relates to a rear projector for projecting an image from behind a screen and, more particularly, to a rear projector capable of adapting to different screen sizes.
2. Related Background Art
With image display apparatus (projectors), there are recent trends toward large screens. For example, the rear projection type image display apparatus is known as one of methods for realizing the large screens. The image display apparatus of this type is constructed to enlargingly project an image formed by an image forming device such as a liquid crystal panel or the like, through a projection lens (projection optical system) onto the backface of the screen (which is a surface on the far side from the user with respect to the screen) and to permit an observer to observe the transmitted image on the other side of the screen. In parallel with the trends toward the large screens of the image display apparatus, image control equipment has been developed for use in controlling an externally connected computer while entering coordinates by direct indication on the screen with an indicator or the like or for use in writing characters, graphics, etc., and has been being mounted on the image display apparatus.
The rear projection type image display apparatus heretofore was constructed to project the image onto the screen by use of a reflecting mirror in order to shorten the depth of the housing. The image display apparatus, as illustrated in FIG. 1 (also referring to FIG. 4), is set up to project an image from a projection optical system for forming the image and projecting it, onto the reflecting mirror 27 placed on a housing back panel 36 and thus project the image onto the thin screen 30 placed on the front surface of the housing, and the structure consists of two parts, the housing 37 having the projection optical system and the reflecting mirror 27, and the screen part 32 having the screen 30.
The image control equipment is an image control device comprised of an indicator for generating a light spot and a detection device for detecting the light spot generated by the indicator, and the detection device 26 is placed inside the housing 37. With these image display device and image control device, the image display position and the image control range for control of image were adjusted in such a manner that the image display position was adjusted relative to the screen part 32 upon installation of the projection optical system and that the position of the image control device was adjusted relative to the screen part 32 upon installation of the detection device.
In the housing structure consisting of the screen part 32 and the housing 37, as in the case of the above conventional image display device illustrated in FIG. 1, however, all the members of the housing 37 must naturally be changed with replacement of the screen part 32 for variation in the screen size.
The housings have been increasing their size with increase in the screen size of the image display apparatus and it is also becoming difficult to design the housings with sufficient accuracy in the relation of process accuracy with deflection of the members themselves and cost. This means that with increase in the screen size the displayed image becomes more affected by deviation between relative positions of the projection optical system and the reflecting mirror 27 placed on the back panel 36, because the increase in the screen size involves a trade-off relation between dimensional accuracy for each member and dimensional accuracy optically required. Part of the image cannot be displayed on the screen in certain cases. It is, however, extremely difficult in terms of the structure to adjust each of the image display position and the detection device 26 after the projection optical system and the detection device 26 have been incorporated in the housing.
An object of the present invention is, therefore, to solve the problem in the above conventional apparatus and provide a projector that is capable of flexibly adapting to change of the screen size and that permits easy adjustment of the image display position or the detection device forming the image control device.
A projector according to one aspect of the present invention is a projector of a rear projection type for projecting an image from behind a screen, which comprises:
a screen part having a screen of a predetermined size; and
a main body part having projection means for projecting an image onto the screen,
wherein said screen part is replaceable with a screen part having a screen of another size different from said screen of the predetermined size.
In the projector according to another aspect of the invention, a projection distance of said projector is variable.
In the projector according to another aspect of the invention, said screen part comprises a reflecting mirror behind said screen and said projection means projects the image via the reflecting mirror onto said screen to display the image thereon.
In the projector according to another aspect of the invention, said main body part comprises detection means for detecting information indicated on said screen.
In the projector according to another aspect of the invention, said information is a position indicated on said screen.
In the projector according to another aspect of the invention, said projection means and said detection means are integrally formed.
The projector according to another aspect of the invention comprises image control means for detecting the information indicated on said screen, by use of said detection means and changing the image displayed on said screen, based on the information.
In the projector according to another aspect of the invention, at least part of said projection means and said detection means is moved to effect positional adjustment of a range in which said projection means projects the image and a detection range in which said detection means can detect the information, on said screen.
In the projector according to another aspect of the invention, said main body part comprises a projection optical system for projecting the image and a detection optical system for detecting the information on the screen, and said projection optical system and said detection optical system are integrally formed in a state in which optical axes of said systems are parallel to each other.
A projector according to a further aspect of the present invention is a projector of a rear projection type for projecting an image from behind a screen, which comprises:
a screen part having a screen of a predetermined size; and
a main body part comprising projection means for projecting an image onto the screen and detection means for detecting information on the screen,
wherein said projection means and said detection means are integrally formed.
In the projector according to another aspect of the invention, said projection means and said detection means are integrally formed so that an optical axis of a projection optical system of said projection means is parallel to an optical axis of a detection optical system of said detection means.
The projector according to another aspect of the invention comprises image control means for changing the image displayed on the screen, based on the information detected by use of said detection means.
In the projector according to another aspect of the invention, a projection distance of said projector is variable.
In the projector according to another aspect of the invention, said screen part comprises a reflecting mirror behind said screen and the image is projected via the reflecting mirror onto said screen to be displayed thereon.